This application proposes to study the molecular basis of post-testicular sperm maturation in the chimpanzee. It is based on the requirement for sperm to undergo a maturation process before they can fertilize oocytes. Essential events in sperm maturation occur in the epididymis where androgen-dependent proteins are secreted into the lumen and interact with sperm. These ADESPs, and the order in which they interact with sperm, are critical for sperm maturation. However, the identity of these ADESPs, their cellular sites and sequence of secretion, and their specific roles in the fertilization process are unknown. Accordingly, the applicants propose: 1) to determine the role of the chimpanzee ADESPs, EPI-1 and EPI-2 isoforms, EPI-2A and EPI-2B, in the fertilization process, using antibodies generated against these proteins in functional, immunocytochemical, and immunohistochemical assays; 2) to identify additional ADESPs using representational difference analysis (RDA) and differential display polymerase chain reactions (ddPCR) on epididymal RNA from androgen-normal and androgen-deprived chimpanzees; 3) to identify those ADESPs that are essential for sperm maturation and for the fertilization process by using antibodies generated against ADESPs in functional assays for fertilizing capacity; and 4) to identify by immunocytochemistry the localization of ADESPs on the sperm surface as an indicator of their effect on the fertilization process, and to determine by immunohistochemistry the sequence in which sperm contact ADESPs along the epididymis as an indicator of the order of events during post-testicular sperm maturation. These studies are essential in understanding primate reproductive function, and may contribute to the development of contraceptive strategies based on interfering with post-testicular sperm maturation. This would permit fertility control in the captive chimpanzee population while not compromising social interactions and the potential use of the chimpanzee population for biomedical research.